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Sterilization Methods

Sterilization Methods

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Sterilization Methods...
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Sterilization Methods
 Infection Control In the Medical Office
Infection control has assumed a greater role in medicine and dentistry than ever before. The Centers for Disease Control (CDC) has issued guidelines for infection control in the the medical, surgical, dental, or podiatric office or clinic. Instrument sterilization is one of the most important parts of office infection control. The cardinal rule of infection control is "Do not disinfect when you can sterilize." The approach is to sterilize all reusable instruments contaminated with blood, or that have penetrated tissue or touched bone (universal sterilization). This is better than to sterilize some instruments and disinfect others and is the safest approach to prevent spreading disease to patients.

sterilizing wrapped instrumentsSterilization is a process intended to kill all microorganisms and is the highest level of microbial kill that can be achieved.
A process cannot be called a sterilization process unless it has been shown to be capable of killing high numbers of bacterial spores, the most difficult of microorganisms to kill. The CDC views steam under pressure, dry heat, chemical vapor and ethylene oxide gas as appropriate sterilization methods.

To assure effective microbial kill with minimal instrument damage and protection to the staff performing the procedures, several steps must be performed: presoaking, cleaning, corrosion control and lubrication, packaging, sterilization and sterilization monitoring.

Usually, material allowed to dry on an instrument is more difficult to remove. If cleaning is delayed, keep the instruments wet in a holding solution. This may be a mild detergent, or an instrument disinfectant or sterilant. Do not presoak for more than a few hours, as the longer instruments remain wet, the greater the chances for corrosion of non-stainless items.

Wear heavy utility gloves when handling contaminated instruments and mixing chemical solutions. Wear protective eyewear, a mask and protective clothing to prevent contamination from splashing of the solutions.

The CDC and the Food and Drug Administration (FDA) state that "Cleaning is the basic first step of all decontamination. You always need to clean before you disinfect or sterilize." Patient debris and body fluids must be removed from the instruments before sterilization. Debris can insulate microorganisms from the sterilizing agent, preventing direct contact and inactivation.

Two approaches to instrument cleaning are hand-scrubbing and ultrasonic cleaning. Hand-scrubbing is directly contrary to one of the principles of infection control (reduce direct contact with contaminated surfaces as much as possible). Handscrubbing of contaminated instruments can create spatter and aerosols and increase the chances for an instrument puncture.

When hand-scrubbing, minimize spattering by scrubbing while the instruments are submerged and then rinse thoroughly under tap water and dry. Drying is very important for instruments that will be sterilized in an unsaturated chemical vapor or in a dry heat sterilizer.

Ultrasonic Cleaning
Ultrasonic cleaning is recommended in place of hand-scrubbing in order to reduce direct staff contact with contaminated instruments. Presoaked or other instruments should be rinsed and then placed in a cleaning basket and submerged in the cleaning solution. For best results, follow the directions from the manufacturer of the ultrasonic cleaner. Place the cover on the cleaner and clean for 6 to 10 minutes or until no debris is visible on the instruments.

Hold the cleaning basket of instruments under tap water and rinse thoroughly. Ultrasonic cleaners cannot be considered sterilizers. Thus, the cleaned instruments are still contaminated. The cleaning solution should be drained and discarded at least daily and the cleaner chamber rinsed and disinfected at the end of the day.

Corrosion Control and Lubrication
Always dry cleaned instruments to be processed through a dry heat, chemical vapor or ethylene oxide gas sterilizer or packaged in a paper wrap. Drying reduces the chances of corrosion and rupture of the paper wrap. A rust inhibitor can be applied to non-stainless items to be processed through the steam autoclave.

Instruments should be pre-packaged before processing through a sterilizer so they will be protected from contamination after sterilization. Use packaging material designed for the method of sterilization to be used. Avoid thin paper bags that allow sharp instruments to protrude. Unwrapping pre packaged instruments at chair side in front of the patient can help build patient confidence about the cleanliness of the office.

Sterilization Time
Sterilization fails when the sterilizing agent--steam, hot air, or chemical vapor--does not contact the processed items for the appropriate length of time. Sterilization requires varying degrees of time, depending on the load, arrangement, packaging material, and temperature as well as the type of sterilizing agent. Follow the manufacturer's direction and define the proper sterilizing time by results of routine spore-testing.

Sterilization Monitoring
Sterilization can be monitored by chemical indicators (color change) but effectiveness cannot. Chemical indicators are strips, tapes and markings on bags and pouches that change color or physical form after exposure to the sterilizing agent. They immediately indicate that the items have been processed through the sterilizer and have been exposed to heat, steam or chemical vapor. Since chemical indicators do not analyze for microbial kill, they should be used in conjunction with, but never as a replacement for spore-testing, which provides the main guarantee of sterilization.

Routine spore-testing (biological monitoring) of the office sterilizer helps assure the quality of patient care. Sterilization failure from improper use or malfunction of the sterilizer increases the chances for spread of disease agents from patient to patient via the processed instruments. Routine spore-testing can detect these failures and alert the office to check and correct packaging procedures and sterilizer loading, operating and functioning. Spore-testing is a very important form of risk management.

Biological Indicators
Biological indicators are the ultimate criteria for monitoring sterilization. The CDC states the proper functioning of sterilization cycles should be verified by the periodic use (at least weekly) of biologic indicators (i.e., spore tests). OSHA recommends following CDC guidelines for standard sterilization procedures.

Proper spore-testing in the medical, surgical, dental, or podiatric office or clinic involves placing the appropriate type of biological indicator (spore test) inside a normal instrument pack, bag, or tray. Biological indicators operate on the premise that destruction of heat-resistant spores implies destruction of viruses and bacteria, which are more easily inactivated. The biological indicator is included in a sterilization load and subjected to the cycle. It is then incubated in a nutrient medium and evaluated.

It is the responsibility of each the medical, surgical, dental, or podiatric office or clinic to assure their staff and patients that products at point-of-use are sterile. Appropriate records should be kept to document sterilization verification.

(1.) Department of Labor, Occupational Safety and Health Administration. 29CFR Part 1910.1030, Occupational exposure to bloodborne pathogens; final rule. Fed Reg 1991,56:64004-182.
(2.) Infection control guidelines. Denver: Office Sterilization and Asepsis Procedures Research Foundation; 1992.
(3.) Office Sterilization and Asepsis Procedures Research Foundation. Infection control guidelines. Denver; 1991.
(4.) Centers for Disease Control. Recommended Infection-Control Practices. MMWR 1993; 42:1-10.

Sterilization Methods Handout
A.   Methods of Sterilization

1.  Physical Methods
Steam Thermal - Autoclave:
Definition -- a self-locking apparatus for the sterilization of material by means of steam under pressure.

Settings for general wrapped items:
Temp. - 250oF Pressure - 20 PSI
Time -- 30 min Setting -- Fast Exhaust & Dry

Settings for bottled solutions:
Always vent bottles to avoid bursting!
Temp. - 250oF Pressure - 20 PSI
Time -- 30 min Setting -- Slow Exhaust

Setting for "Flashing" an unwrapped instrument:
Temp. - 270oF Pressure - 30 PSI
Time -- 4-7 Min Setting -- Fast Exhaust
Notes -- The above are general steam autoclave settings. Different models may operate with varying settings. Always refer to the appliance literature before operating a new piece of equipment.

Use on materials that cannot be sterilized by heat or chemicals
Radiant energy destroys microorganisms

Filtration -- is a method utilizing filters capable of screening out microorganisms

2.  Chemical Methods
Ethylene Oxide Gas
Colorless gas at room temperature
Odor similar to ether
Very toxic and irritating to skin and mucous membranes
Microorganism destruction is caused by a chemical reaction
Materials sterilized need to be aerated in well ventilated room or placed in an aerator.
Length of time required for aeration depends on items sterilized.
Effective sterilization is dependent on concentration of gas, exposure time, temperature, and relative humidity
Hazardous chemical, use great care

Cold Sterilization
Instruments should be completely dry before soaking to prevent dilution
Instrument soaking solution - 10-20 minute emersion only disinfects
Incomplete destruction of spores, unless soak is for 10 hours
Examples: Instrument Germicide (Phenol and Ethyl alcohol), CidexTM (Glutaraldehyde)
Most require thorough rinsing before using instrument
Contact time required varies with product used

B.   Sterilization Shelf Life of Packaged Supplies

1.  The following wrapped items, if carefully maintained, are sterile for up to one (1) month:
Double cloth wrapped instruments
Double paper wrapped instruments
Inexpensive peel pouches for gauze sponges
NalgeneR saline bottles

2.  Two (2) packaging methods are sterile for up to six (6) months:
MonarchR Instrument Canisters -- Special box system with single use filters for use in steam autoclaves
Sterility Maintenance Covers -- Sealable plastic covers to place over freshly autoclaved and cooled packs to extend shelf life by diminishing air penetration

3.  Heat sealed packages commercially prepared in tube or peel pouch form may be considered sterile for up to one (1) year.

C.  Sterility Check List

Before assuming a pack is sterile, always evaluate the following before opening the pack:
Expiration or sterilization date
Indicator color change
General condition of wrapper and how it had been stored
Always check for holes or moisture damage


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